1. Field of the Invention
This invention relates to electronic devices, such as electronic calculators, which are battery operated and incorporate one or more liquid crystal displays.
2. Description of the Prior Art
With the advent of integrated circuits, particularly Large Scale Integrated Circuits (LSI's) vast new potential markets have been opened for miniaturized electronic devices, such as electronic calculators and digital watches. These devices are battery operated and consume amazingly small electrical power. For example, a hand-held electronic calculator may consume only 0.5 milliwatts when operating. The batteries presently used to operate such devices are silver oxide batteries which have relatively large milliampere-hour capacity in a small volume. Such batteries have been used for years in hearing aids.
There are two types of digital displays used in such calculators and in electronic watches. Those two types of displays are Light Emitting Diodes (LED's) and Liquid Crystal Displays (LCD's). LED's rely upon light emitted from a p-n junction in a semiconductor material, such as galium arsenide, when a voltage of the proper magnitude and polarity is applied across the junction.
LCD's rely upon a completely different phenomenon. Certain molecules, called nematic molecules, exhibit solid crystal characteristics, such as light polarization and electromagnetic vector rotation, when an electrical potential appears across the liquid. By combining shaped electrodes, light polarizing sheets and a reflector, light incident upon the display can be selectively reflected, i.e., in accordance with the disposition of the electrodes to which an electrical potential has been applied. The light which is not reflected is simply unused and lost through absorption or otherwise. The power required to orient the liquid crystals is miniscule. Further, as has been indicated, the power to operate the logic circuits is also miniscule.
Therefore, it is an object of this invention to provide a combined liquid crystal display and photovoltaic converter which will self-power the display and its associated circuits, with or without battery storage capability.
It is a still further object of this invention to provide a digital display-power generating device which utilizes substantially all of the light incident upon it.
It is an additional object of this invention to provide a self-powered electronic calculator.
It is a still further object of this invention to provide a self-powered electronic watch.